1. Field of the Invention
The present invention relates to improvements in a lubricating system for an automatic transmission, and more particularly to a lubricating system which efficiently supplies lubricating oil to elements of an automatic transmission.
2. Description of the Prior Art
It is well known that automatic transmissions for automotive vehicles are provided with lubricating systems therein for lubricating elements of the automatic transmission such as gears, bearings and friction elements. Such a lubricating system is disclosed, for example, in Japanese Utility Model Provisional Publication No.1-80853 and on pages A-1 to A-38 of a service manual "NISSAN AUTOMATIC TRANS-AXLE RL4F03A TYPE" published in May 1989. In these conventional lubricating systems, lubricant pressurized by an oil pump is fed to a main passage formed inside of input and output shafts through a control valve assembly, and supplied outwardly to elements of the transmission.
However, with these conventional system, lubricant is simultaneously and usually supplied to planetary gear sets, bearings and friction elements. Although the planetary gear sets and bearings need to be usually lubricated, the friction elements may only require lubrication during a shift. Accordingly, it is not effective to usually supply lubricant to the friction elements since the oil pump is excessively operated and the power loss due to the stirring loss of the friction element is generated.